Main Street is no place for the weapons and machines of war. But the needless militarization of police departments in cities across the country has been going on for decades.

Ever since riots in the 1960s, attacks by radicals in the 1970s, and the fight thereafter against drugs, local authorities have sought and obtained battlefield-style equipment, mostly with the help and encouragement of the federal government.

Beginning on Sept. 11, 2001, the war on terror boosted to an even greater degree the arming of U.S. municipalities.

Now President Obama has ordered a long overdue review by Washington of the arsenals assembled by police in American cities and towns.

"There is a big difference between our military and our local law enforcement, and we don't want those lines blurred," Mr. Obama said. "That would be contrary to our traditions."

His intervention is clearly warranted.

The president acted after violent confrontations between protesters and highly armed police in the St. Louis suburb of Ferguson, Mo. The disruptions, which followed the police shooting on an unarmed black teen, were widely televised.

In the small predominantly black town, police and National Guard units in riot gear responded. They carried assault rifles, rolled out armored vehicles and fired tear gas.

The Ferguson Police Department had acquired two Humvee armored vehicles and other military gear for free under a Pentagon program that distributes surplus equipment at the request of states and cities nationwide.

Since 2006, the Department of Defense has thus been the source of more than $4 billion in armored vehicles, weapons and items for civil stockpiles.

What's known as the 1033 program began in 1991 to help equip police forces in the war on drugs. It was revamped in 1997 to include counterterrorism needs.

Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee, said his panel will seek to determine if the Defense Department surplus is being used properly.

"We intended this equipment to keep police officers and their communities safe from heavily armed drug gangs and terrorist incidents," said Mr. Levin.

Rep. Hank Johnson, D-Ga., plans to introduce legislation limit the kinds of military equipment that can be transferred to local police and require states to account for all equipment received.

There are reports that some weapons and other equipment distributed to police have gone missing.

Not just Mr. Obama and his Democratic allies are concerned about the domestic impact of military weaponry.

In a column for Time magazine, Mr. Paul wrote: "Washington has incentivized the militarization of local police precincts by using federal dollars to help municipal governments build what are essentially small armies - where police departments compete to acquire military gear that goes far beyond what most of Americans think of as law enforcement."

Back in June, the American Civil Liberties Union warned against the excesses of heavily armed Special Weapons and Tactics (SWAT) teams deployed by police departments.

"Neighborhoods are not war zones, and our police officers should not be treating us like wartime enemies," said Kara Dansky, senior counsel for the ACLU.

The worry is that militarization can encourage police officers to adopt a "warrior" mentality and think of the people they are supposed to serve in an us-against-them fashion.

What's needed are strict standards for the transfer of military weaponry to police departments, along with better accountability, training and limits on deployment.

Cops on the beat are not armed members of an occupying force.

They are dedicated public servants who are there to keep law and order for all of us.